Tesla Patent Outlines Sensible Approach to Cabin Heating

Cabin heating in vehicles with internal combustion engines is simple because the engine generates lots of waste heat. Pure BEV’s on the other hand don’t have this source of waste heat and so they must rely on the battery as a source of energy for heating. Using the battery for heating lowers the range. In extremely cold environments, we could see as much as a 50% loss in range for a battery electric car. That’s a big disadvantage.

Early LEAFs’ Resistive Heaters Used A Lot Of Power To Heat The Cabin

The early Nissan Leafs (pre 2013) used resistive heating. Resistive heating is probably the most inefficient way to heat the cabin. In 2013 the Leaf incorporated a heat pump and this mitigated the effect on range in cold weather. When operating in electric mode the Volt’s cabin heating is purely resistive so the Volt loses significant range in cold weather if the ICE does not run. Gen 2 Volt also retains just pure resistive heating in EV mode.

Is there any waste heat floating around in a BEV that could be used for cabin heating?

Yes there is. It is waste heat from the electronics and from the traction motor.

Tesla has a patent on just such a system. The schematic from the patent describing the system is shown below.

Tesla patent shows waste heat from the drive motor and electronics being used to heat the cabin

A simplified version is shown below:

Simplified version of patent schematic

Heating Efficiency Is Extremely Important In Cold Temperatures For BEVs

The patent shows 4 separate cooling loops. The top cooling loop is a glycol loop that cools the drive motor and electronics. In hot weather this loop just rejects heat to ambient from a radiator in the front of the car.

The loop right below the electronics cooling loop is the cabin heating and cooling loop. This glycol loop can cool the car via the refrigerant loop (shown below the cabin loop) or in heating mode the cabin loop uses a resistive element for heating

The ingenious part is that the motor/electronics loop can communicate with the cabin heating loop via some flow control valves. With the 2 loops connected, waste heat from the motor and electronics can be used to heat the cabin with the resistive heating element used as a second source of heat. Scavenging the waste heat lowers the load on the battery and increases range.

A simplified version of the Tesla patent in “waste heat cabin heating mode” is presented in the figure below.

We don’t have positive information from Tesla itself, however based the following write up in an excellent Tesla Motors Club article it appears that this patent probably is used in the production Model S.

The Model S cabin heater has two (hidden) modes. If the drive train is cold, all heat comes via resistive heaters, which can draw up to about 6 kW. That’s a lot of power.

As you drive the car, the drive train will naturally heat up. Once that happens, Model S uses the drive train coolant to help heat the cabin. Essentially it takes waste heat from the motor and inverter and uses that to heat the cabin. This makes a huge difference to the power consumption – a fully warmed-up car will only need 1-2 kW to keep the cabin warm even in extreme cold conditions. In comparison, the original Tesla Roadster needs 4 kW to keep its tiny cabin not-terribly-warm using only resistive heaters. This is a big advantage of Model S engineering that Tesla never talks about!”

The upshot here is that cabin heater power consumption gets better quite dramatically after you’ve been driving for a while.

No Heat Pump?

Let’s look at a simplified sketch of the Refrigerant loop in the Tesla patent.

There are no reversing valves shown in the Tesla patent. Also there are to expansion bypass valves shown in the patent. Therefore, there is no heating mode in the Refrigerant loop.

That’s the patent but does the Model S incorporate a heat pump in production?

Again we have no direct information from Tesla but all indications from Google search suggest that there are no reversing valves and therefore no heating mode for the refrigeration system in the model S.

What could Tesla do in the upcoming Model 3 BEV to improve on their heating scheme?

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Seeing as this is done all the time in commercial ventures, and seeing as there is no refrigeration occurring, I don’t see how much of this is ‘patentable’. I’m more interested in seeing the cars’ power consumption in weather that I personally experience, and I’d think many in similiar climates would also. But in the “S”‘s case, what is the loss just sitting there in very cold weather, and “very cold” is not 45 degrees F. Now, many companies have come out with ‘cold-weather’ heat pumps that actually work very well at 20 degrees Fahrenheit, and work down to below 0 degrees F. Some of the ‘absorption heat pumps’ that run on natural gas actually extract an amazing 104% of the Natureal gas input as building heat (obviously the ‘flame’ is outside, and 104% efficiency means, that in the area of the flame, the atmosphere is leaving COLDER with the flame on than OFF!!). So excuse me If I’m a bit underwhelmed. As far as the Volt and ELR having resistance heating, I’m finally resigned to the fact that the resistance heating in those cars isn’t really meant to be used. The primary source of heat in the car is… Read more »

With so much prior art, it isn’t patentable and hasn’t worked well either I might add.
On how to do it is simple, put a lot more insulation and switch most windows to plastic except the windshield.
Then a heat pump working off the cabin exhaust air.
Motors, controllers just don’t give off enough waste heat and lucky to collect 1/4 of that.
And spend more money on the heat exchangers making them more efficient alone could cut power needed by 30-50%.
Do all these and heating/AC is a breeze.
Getting more tricky just heat the driver, passengers with a insulated ‘tent’ with arms with heat coming up from the seat.
In really cold areas wear an electric heated snowsuit to save range.
I’m in Fla so a heated seat has always kept me warm. But my cars are composites so not as much a problem as metal.
Try a truck/RV bedpad made for 12vdc or a electrically heated jacket.
I’ve converted electric blankets to 12vdc and use as a wrap or buy them in RV stores, sites are other ideas.
I use these at home too letting the house get into the 60-50’s but staying toasty wrapped in an electric blanket.

The local Nissan Dealer jokes that the ONE Leaf owner of theres wears a Snowmobile suit in the wintertime.

The problem that you southerners really don’t realize is you HAVE to heat the cabin – otherwise you cannot see period out of the windshield.

I had a 64 vw as a teen, along with TWO ice scrapers. One to scrape the frost while driving along on the outside, and the other to scrape my breath off the inside of the windshield while driving along. My father thought it would be cool to put a cherry bomb muffler on the thing. Unfortunately, it had no heat exchanger for the cabin heat as did the original.

Sometimes the greatest value of a patent is not in the advantage gained in profiting from IP, but in preventing legal and business costs associated with patent trolling. The heat pump in the Leaf doesn’t help at low temperatures, which is when it’s most needed due to the other inefficiencies of low temperature operation. There are heat pumps for homes that help in low temperatures, but there aren’t lots of examples of high performance heat pumps in BEVs that say that they can be translated to automotive use. BEV utility is limited by degredation and its performance in adverse conditions. Living as I do in a location where winters temperatures are regularly below 10F, a system that assists in those low temperatures could be more important to me than a system that helps more the rest of the year. It would all depend on the range of the BEV, which would determine its usage pattern. The Volt doesn’t actually have an approach of using the engine to provide cabin heat. It just has two magic numbers below which it will run the engine to provide cabin heat. If it were an _actual_ engineering approach instead of an engineering failure, the… Read more »

Gold? The B-class has a front defrost element, similar to the way typical rear defrost works on many cars. That’s all that is needed, IMO. The filament can be thin, and save a ton of watts.

Tesla uses much bigger motors, from which heat can be harvested. It is impressive to think a 6kw draw can become 2kw, using their glycol loops. I hold by my own experience, backing this up when I say the first ~20 miles can be as low as half a mile per KWh, but afterward, yes, even in very cold weather on a highway, the Model S does an outstanding job of regaining its usual 2.5-3.5 mile per kwh (~300-350 watt hour/mile). You first have to warm the battery and motors, from 10, or 20F degrees.

PS – I am having ‘not responding’ issues with inside evs website, these past couple days. There might be some advertising script. Can’t figure it out, but this text was pasted.

Now I wouldn’t have all that complication even if I didn’t have a 12 to 120 volt inverter (which is the way the problem would be solved today).

I’d use the 3 phase from the alternator before it went through the six-diode bridge, and send it through a small step up transfomer to provide 120 volt 3 phase for the gold. Since the alternator regulator DC output is regulated for the car battery, indirectly the AC output is also therefore regulated, and needs no further controls other than a relay ahead of the 3phase stepup transformer.

If that requires more explanation, think of the existing 6 diode bridge as a ‘voltage clamp’ keeping the voltage output from getting too high.

Since the gold wires get first dibbs at the juice, the battery may have to discharge a bit while the defroster is on and the gold wires are sucking up all the juice from the alternator which may not put out quite enough to run both loads if the engine is just idling.

It takes 4 kW to heat my entire house, an old one with single pane windows all around. It takes 1 kW space heater to heat a bathroom. It would seem car’s cabin would be closer to bathroom, but let’s say 2 kW.

At 2kW, car would have to be traveling at 20 MPH or less. If this is considered, why not 1 MPH case (freeway speed in LA), and say heating takes 90% of range?

A more realistic case is heat/cool taking about 20% to 25% of range. That’s 8kW, average speed of about 45 MPH combining highway + local. Then SparkEV would get 62 miles range; bad but not awful.

Not sure about your “house heating” math, I guess 4 kW usage depends on your location. George is saying “extremely cold”, given where the Spark EV is sold, I’m guessing the prairies or Alaska is not your home, (= Heating by electricity in the far north would be very, very expensive/power consuming. — Just to speak to George’s point though, I had LEAF#2 (MY 2011) back almost 5 years ago, and it had the original resistive heating. I was caught up in the Canadian Shield one day on a record low (ironically after just after having spend a month or so in Florida with unseasonably high temperature) when the temperature dropped to around -50F/-45C. I netted 27 miles from full (although I had 1 bar left when returned), so maybe ~32 miles total. That was a ~62% loss, although I would suggest this was the most extreme case you could ever find for EV operation in the worst/least efficient cabin heating system on the market. Of note: the “battery temp” bar ended the trip at 1 bar and the regen was of course disabled for entire trip. Also the heating system had zero chance of catching up, it was on… Read more »

If you want an extreme case, all you need to do is a scenario in which the EV is caught in a traffic jam, with traffic moving very slowly, but weather conditions are so hot or so cold that the driver runs the heater or A/C. In that case, if it takes hours to get out of the traffic jam, it’s possible to use up 90% or more of the battery pack’s energy just running the cabin heater and/or the battery heater.

More realistically, the rule of thumb is that you can lose up to 30% of range in very cold conditions… even for those in, for example, Norway. In my opinion, the citation of 50% loss is an outlier that will be so rare as to be inapplicable for most drivers.

GM considered using the electronics waste e original Volt. In the end, the additional complexity and cost it added made them avoid it.

I still think it has merit in some form, either heating the battery in the cold weather or the cabin.

Part of me thinks the real issue with efficiency here is that the vehicles still heat a coolant loop. If they could make a heater that heat the air directly, it would be much more efficient for short trips. Otherwise you spend a ton of energy heating up coolant that then never gets used. On longer trips it becomes less significant to do it in this manner.

The battery needs a little help getting warmed up from a cold soak but enough waste heat is generated under most driving conditions to maintain it’s temperature or even require cooling. Somewhere around 93% efficiency at an average of 20KW is 1.4KW of average waste heat internal to the battery.

Ah here we are. This is my favorite subject, because we had the coldest winter in days/degree since nobody know last year in Québec. A harvesting loop is a must around here if you want to preserve your range. Inverter and motor waste together about 20% of the energy used for traction. 98% of it is heat. At 100 km/h it’s about 20 kW pull by the motors and that make 4 kW of heat that you could recover. But when you have a cold battery, you can’t regen any breaking power because the battery can’t absorb it. But it would be possible and very welcome to use this available power to heat robust element in the heating loop just to kind of store it in. And of course, like the BMW i3, get a software feature to pre heat your battery at a decent working temperature. I mean in the upper workable spectrum or more, like 28 c° and use this store heat in the heating cabin loop to avoid draining electric energy instead. Better insulation, some solar harvesting, and a better sealed cabin against air infiltration with a good air recuperation system would be a great advantage. Heat… Read more »

You don’t need batteries to store heat or cold the only issue is the economics and safety of the storage technology. So very few people use batteries in their home to store electricity as heat as time tested mechanisms exist, but I think the impediment and solution to all these problems is cheaper batteries and bigger battery packs.

I haven’t been clear I guess.
I’m proposing to use battery as an energy storage and an heating storage simultaneously.
Because of their high mass and compactness, they also have an high thermal inertia that would be better used as doubling the total energy storage. Cold or hot, but they probably work better with some heat, below 28c° or else?
85 kWh battery could store a lot of kWh of heat.
I guess 30 kWh or more depending on the condition.
How about that increase in capacity?
At much better $/kWh than any chemistry available today also.

The problem with using the thermal mass of the battery pack to help with heating the car, is that this means you must move the heat out of the battery pack into the passenger cabin.

The more cooling that happens, the colder the battery pack gets. This is a bad idea for several reasons. Even if you don’t lower the temperature enough to seriously affect battery function, repeatedly heating and cooling the battery pack will lead to faster aging of both battery cells and the electronics.

One of the reasons that Tesla battery packs hold up so well over time is that they are designed to “baby” the battery cells. Using the pack as a heat/cold sink, to help with cabin heating/cooling, would do the opposite.

The problem in the wintertime is to get heat TO the battery, not take from it.

Most of the juice I used in my Roadster in the wintertime was to try to keep the battery warm enough to charge. It would nonsensical to take heat from it since its so hard to get heat into it in the first place.

This is because the pack hasn’t been insulated on purpose.
My 2012 Leaf sit in a steel tub with all the underneath expose to the pavement.
That was made to cool it free in seasoned location, leaving the baking problem in parking sunlight that we all know and that Nissan would have prefer avoiding.
This set up have also adverse effect in winter because it cool too much the pack, so much that the system have to sometime use the internal heating to keep the pack in thermal shape.
This is just wasted energy.
A well insulated pack with a thermal control mechanism would do great both for the optimal capacity of the pack and also avoiding scavenging precious kWh that could be used to the cabin temperature control.

An ac is needed for cooling so it can as well be used for heating. On the other end there is no reason to copy paste the old systems of compressors based ac, in a similar situation the navy switched to thermoacoustic cooling for its light weight radar systems. Thermoacoustic doesn’t use freon gas which is an extra advantage. Actually thermoacoustic systems can heat, can cool but they can also serve as an emergency power supply in generator mode if you supply it with fuel. It has the potential to be a 3 in 1.

The i3’s (BEV only) heat pump is cleverly plumbed to be able to cool and/or heat its battery pack, electronics, and cabin. But below -10ºC, a heat pump doesn’t heat effectively, so a resistance heater augments the heat pump. But resistance heaters are very inefficient, so another heat source is needed to preserve range. Below -10ºC, the waste heat from the drive motor and electronics would take quite a while to be effective heating the cabin, so a hydrocarbon heater (alcohol or diesel) should be available in very cold climates. For some reason, no EV manufacturer offers one as an option. Instead, EV drivers in really cold weather have the choice of preserving their range or being comfortable. A hydrocarbon heater would eliminate this dilemma while producing very low levels of hydrocarbon and CO2 emissions.

I don’t find it any surprise that no EV maker offers an EV with a cabin heater fueled by gasoline or kerosene or whatever. Many or most of those who buy EVs do so with the intention of reducing or eliminating as much of their petroleum usage as possible, so a petroleum powered cabin heater would run contrary to that. It is a good practical solution for those who live in very cold climates, but it would be very bad for the car’s public image.

Art Isbell said:

“…while producing very low levels of hydrocarbon and CO2 emissions.”

Certainly the pollution and CO2 emissions of a petroleum fueled cabin heater would be significantly lower than powering the entire car that way, but I question that the exhaust would have “very low” levels. I suppose it depends on what you consider “low”, which obviously is a subjective value rather than an objective one.

I fully agree with Art Isbell on that. In a cold climate there is simply no better solution.

The amount of pollution produced by such heaters is minuscule. People even use them indoors. Unlike ICEs, or even electric heat pumps, the heaters don’t produce noise or vibration, don’t require maintenance, and are light and cheap. As for the image – it would be better for mass adoption of EVs if they were not associated with radical environmentalism.

On a car he probably mean an outside exhaust with a heat exchanger instead of a kind of candle in the cabin.

Ethanol is used in the window washing spray, so a similar small tank for heating with it could be used in extreme cold weather, perhaps would also be possible to use a miniature wood pellets stove as a top enviro alternative, but Ethanol seems fair enough.

Pre-heating the cabin (especially de-frosting) is the main issue as it uses so much energy if done solely by resistive heating when you first get in the car. Some EVs can do this from mains power whist still plugged in. Quite why any EV would be designed not to is a complete mystery. EU Mitsubishi i-MiEVs have an *option* for this but its Peugeot and Citroen sisters do not. I have resorted to mounting a mains fan heater on a bit of ply and sitting it on the back seat switched by a radio controlled socket. A few lines of extra code in the car’s computer could achieve the same thing using the existing charging lead. But really, as others have said, electrically heated seats and front and rear windscreens should be a basic spec for EVs sold anywhere where the temperature regularly falls below 5 degrees C.

A heat pump can work bellow minus 10ºC but it becomes less effective although its COP is still higher than the 1 value of a resistor. If the evaporator is a multiple sequential version the icing problem is solved in a continuous way since there is always one part in defrost mode while the others are working. That is however more complex so many heat pumps switch to a resistor assistance to avoid the many idling during the 100% defrost cycles instead of resorting to partial 25% defrost cycles. On a car however the situation could make partial defrost more interesting.

What are the efficencies of the motor in a Model S and in other BEV like i3, Zoe, …? If they say that the motor in the Model S produces some heat, maybe there’s room for efficiency improvements so this complex system could be simplified?

I would like fact and data for this comment and the one you made at 8.36 am for the efficiency of the equipment.
As far as I know, Tesla use a simple three phase motor that is pretty much the most efficient you can find.
But only at a certain R.P.M. that isn’t the one that’s always running.
Beside controlling a three phases motor acceleration and regen is much more complicated than an PMM that just about every other manufacturer choose.

And for the other comment, top quality inverter don’t get any better than 90% efficiency yet.

M is right. PM synchronous motors are a few percentage points better efficiency since there are zero rotor current resistance losses simply because there are zero rotor currents.

My solar inverters are a minimum of 97% efficient with a more typical 98% efficiency.

That is why worrying about using the DC coming from the solar panel for utilization equipment is a non-starter. It is simply much more convenient to use the plain old AC the house was wired with anyway.

All Leafs did not get the newer heat lump style heater in 2013. Only SV and SL models from 2013 and up have the heat pump. My 2015 Leaf S has the same resistive heater that my 2012 SV had. And when its below 32degrees, the heat pump heater isnt any more efficient. Below 32 degrees, the heat pump heater is basically working as a resistance only unit. Ill use the heated seats and heated steering wheel only until it gets really cold. Once its well below freezing, ill use the heater(defroster) intermittently to keep the windshield clear. Oh how i wish for a electrically heated windshield like other cars have had. The heater draws too much juice and turns my 90-100 mile summer range into only 50 on the coldest days.

I always thought the little energy wasted in the electric machine might even be enough to heat a car. The argument of reusing the lost energy in an ICE, is just stupid. If one would sit down with ones calculator, the one would very soon understand that if you would pump all the wasted ICE energy into the car, the car would not be a nice place to be…

What I find frustrating is, that all the glycol lines for Heat/AC aren’t insulated. In my iMiEV, that would have required about 10$ in additional material at manufacturing but is a pain in the neck to do a Joe Homeowner afterwards.
They should all have the lines insulated (Period).

One of my favorite quotes: “In theory, there’s no difference between theory and practice. In practice, there is.” The schematic shown in this Tesla patent show an idealized, theoretical case. In practice, there may not be all that much energy savings. Art Isbell was entirely correct in saying: “But below -10ºC, a heat pump doesn’t heat effectively, so a resistance heater augments the heat pump. But resistance heaters are very inefficient… the waste heat from the drive motor and electronics would take quite a while to be effective heating the cabin…” This is a good summary of the dilemma. Electric motors and inverters are so very efficient at using energy that there isn’t that much waste heat available to heat the cabin. And since there isn’t that much available, it takes that much longer for things to heat up sufficiently to heat the cabin to a comfortable temperature. For that reason, if no other, a BEV needs a resistance heater to supplement the use of heat pumps and drawing heat from the powertrain. I don’t see this situation changing. Basic physics severely limit how much heat can be generated, and how fast, by using a heat pump and/or harvesting waste… Read more »

I have found with my Model S, that the best thing is to warm the car while its still plugged in. That way all the cabin heating is done without consuming any energy from the battery. I believe the Tesla also warms the battery when you remotely turn on the climate control. I’m not sure if the Leaf or Volt have this feature.

The other thing that not many people realize is that air density plays a significant role in reduced range in cold weather. Dry air at 30 F is about 10% more dense than 70 F air at 50% humidity. This denser air translates to increased aerodynamic drag.

Well, I like few of the suggestions listed here. All PEVs should have direct heating of windshields and all windows and mirrors. In addition, all seats and steering wheel should be heated/cooled. But I don’t believe in “wearing” a heated jacket in the cars. I seriously doubt most people would accept that. Now, a clean fuel heater using clean burning alcohol is perfectly acceptable in extreme cold climate. Make it an option and see if people are willing to buy it. Lastly, the “regen” power should be converted to heat in extreme cold climate. When battery is full or cold, most BEVs can’t regen so it is wasted power. Even with regen, the max recoverable power is only about 60% at best. But the recoverable heat from regen can be nearly 100% as in resistance heating. So, it is almost free power to recover. Typicaly cars can easily regen at 30kW to 60kW range. It won’t last long with short duration but a “thermal masses” can be built into the system to absorb the peak power. For extreme cold stop/go traffic, it should work well. I am surprised no EV maker has made that an option.

This should be done for all EV.
I mean, everything is already there, the resistor, the regen, so why not throw the regen in the resistor when needed.
It would also probably be more effective to always heat up the resistor in cold urban driving.
So why not a manual switching option?

This only works because tesla drive train is inefficient (compared to other electric motors). Normal city driving needs only 10-14kWh/100km. But average speed is 35km/h. Meaning in one hour of city driving you use around 3-5kWh. Electric (motor) can be build with 95% efficiency, controller 97%, battery 95%. Meaning around 13% of energy used is heat.

In one hour of city driving you can use less than 0,7kWh for heating if your drivetrain is efficient and you can manage to use all for cabin heating. Not worth the effort.

At highway speed it might be different since you need 2-3 times the energy. But it is not a game changer, its a very expensive solution to gain 10% more range in the worst conditions.

In electronics, heat generation is a sign of poor efficiency because of resistance. Nanotechnology is now being applied in engineering and new advances in battery materials we will see incredible efficiency gains in electric vehicles and the battery power density. Range and battery charge cycles will increase, weight, price and recharge time will decrease. Once this occurs, we will have so much storage capacity in our cars we won’t need to worry about cab heat. 5 to 10 years. Elon is all over it and will advance battery tech exponentially and mass produce it economically.